1. Field of the Invention
The present invention relates to a honeycomb structure.
2. Discussion of Background
In a known honeycomb catalyst used for converting exhaust gases from automobiles, a layer made of a material having a large specific surface area such as activated alumina is formed on the surface of a honeycomb structure made of cordierite and a catalyst such as platinum is supported on the layer. Besides, in a known honeycomb catalyst used for converting exhaust gases from diesel engines, a NOx occluding agent is further supported on the layer to treat NOx in an excess oxygen atmosphere.
However, the NOx occluding agent is likely to occlude SOx more stably rather than NOx, resulting in a SOx poisoning phenomenon where the NOx occluding agent occludes Sox to thereby interfere with a proper occlusion of NOx.
In view of this, JP6-58138A discloses a sulfur capturing device that is composed of a sulfur absorbent and a casing surrounding the sulfur absorbent and arranged in an exhaust gas passage on an upstream side of the NOx occluding agent. As an example of the sulfur absorbent, at least one substance selected from alkali metals such as potassium, sodium, lithium, and cesium, alkali earths such as barium and calcium, and rare earths such as lanthanum and yttrium and a noble metal such as platinum are supported on an alumina carrier. Furthermore, a honeycomb structure as described in WO05/063653A is disclosed.
The contents of JP6-58138A and WO05/063653A are incorporated by reference herein.